1. Field of the Invention
The present invention relates to a fuel cutoff valve installed on the upper portion of a fuel tank for the purpose of shutting off communication of the fuel tank with the outside by means of opening or closing of a connecting passage that connects the fuel tank interior with the outside.
2. Description of the Related Art
A fuel cutoff valve is disclosed in JP-A 7-279789. Specifically, the fuel cutoff valve is mounted on the upper portion of a fuel tank, and comprises a casing having in the upper portion thereof a connecting passage for connection to the outside (a canister), a float for increasing or decreasing buoyancy and rising or falling according to the fuel level within the valve chamber, and an upper portion valve body installed in the upper portion of the float. The fuel cutoff valve is configured such that the float increases in buoyancy due to a rise in fuel level in the fuel tank, and the upper portion valve body integral with the float rises, thereby closing off the connecting passage to halt the flow of fuel to the outside.
The upper portion valve body is a flat plate valve body, and is supported on the upper portion of the float by positioning the center portion thereof on a projection of conical shape projecting up from the upper portion of the float. By means of this design, in the event that the float should tilt due to leaning of the vehicle or other cause, the upper portion valve body will tilt on the conical projection and become seated in the seal portion of the connecting passage, i.e. the upper portion valve body maintains a horizontal attitude corresponding to the attitude of the float, to afford enhanced sealing.
However, the upper portion valve body is susceptible to being supported by the projection of the float in an attitude of displacement away from the center of the upper portion valve body. A resultant problem is that the attitude of the upper portion valve body is not stable, so that sealing ability declines due one-sided contact with the seal portion of the connecting passage. As one design for addressing this problem, there has been disclosed a fuel cutoff valve comprising a float and an upper portion valve body positions on the upper portion the float, with a recess in the upper portion valve body being supported oscillatably on a projecting portion of the upper portion of the float, so that the upper portion valve body is maintained in the horizontal attitude with respect to tilt of the float (U.S. Pat. No. 6,758,235). However, a problem with the fuel cutoff valve is that a projection of the upper portion valve body is point-bearing and has a conical shape in order to stabilize the attitude, and when the distal end thereof becomes worn with service for an extended period, there is a drop in the force restoring the upper portion valve body to the horizontal position.